Eye preferences in capuchin monkeys (Sapajus apella)

Area of Science:

• Primate behavior
• Comparative psychology
• Neuroscience

Background:

• The valence hypothesis suggests hemispheric specialisation for emotional processing: left for positive, right for negative.
• Visual information is primarily processed by the contralateral hemisphere, implying eye preference may reflect emotional valence processing.

Purpose of the Study:

• To investigate if capuchin monkeys exhibit systematic eye preferences when viewing stimuli of varying emotional valence.
• To test the valence hypothesis and its link to functional hemispheric specialisations in a non-human primate model.

Main Methods:

• Eleven capuchin monkeys viewed images categorized as positive or negative.
• Eye preferences (left vs. right) for viewing stimuli through a monocular hole were recorded.
• Looking behavior (direction, number, duration) and arousal behaviors were documented.

Main Results:

• Individual capuchin monkeys showed eye preferences, but no population-level consensus emerged.
• No significant differences in looking behavior were found based on emotional valence.
• Negatively valenced stimuli elicited significantly higher arousal behaviors than positively valenced stimuli.

Conclusions:

• The study's findings do not support the proposed relationship between eye preferences and emotional valence processing or hemispheric specialisation in capuchins.
• While stimuli were emotionally salient, eye preference did not correlate with valence.
• Further comparative research is needed to understand the evolution of lateral biases in emotional processing.